Carbon dioxide provides an environmentally friendly solvent system for many reactions. For example, U.S. Pat. No. 5,739,223 to DeSimone describes methods of making fluoropolymers in carbon dioxide systems, U.S. Pat. No. 5,618,894 to DeSimone et al. describes nonaqueous polymerizations of fluoromonomers in carbon dioxide systems, and U.S. Pat. No. 5,679,737 to DeSimone et al. describes heterogeneous polymerizations in carbon dioxide systems.
Unfortunately, carbon dioxide has not provided a useful solvent system for enzyme catalysis. The pH of liquid or supercritical carbon dioxide is typically in the range of 4 to 5, which denatures most proteins or peptides. Hence, it would be extremely desirable to have a means for carrying out enzyme catalysis in liquid or supercritical carbon dioxide.